In the production of vinyl siding panels having the appearance of rough-sawn cedar shake shingles, for example, as disclosed in U.S. Pat. Nos. 3,593,479 and 5,455,099, it is known to injection mold the panel or vacuum-form a precut sheet and then trim and punch and form the edge portions of the sheet, to form a hook-shaped lower portion along the panel and an upper portion which defines a groove and forms a nailing flange. It is also known to extrude or form a flat sheet of plastics material and then direct the sheet onto the upper run of an endless flexible belt conveyor for vacuum-forming the sheet, for example, as disclosed in U.S. Pat. Nos. 3,982,868 and 5,314,325. The endless flexible belt is constructed of a porous material and defines cavities into which the hot plastic sheet is sucked by a vacuum source under the upper run of the endless belt. The door sheet is then cooled and cut at longitudinally spaced intervals to produced vacuum-formed garage door panels or other articles. It has been found that the endless flexible conveyor belts for producing vacuum-formed articles are expensive to construct, have a relatively short service life and do not conduct heat rapidly away from the vacuum-form sheet.
The present invention is directed to an improved method and apparatus for continuously producing elongated plastic siding panels each having a series of separate shingle panels, and which apparatus is simple and dependable in operation and provides for an extended service life for producing a high volume of siding panels. In accordance with a preferred embodiment of the invention, a flat sheet of plastics material or polyvinylchloride is extruded with a substantially uniform thickness and is directed onto the upper run of an endless vacuum-forming conveyor. The conveyor includes a pair of endless flexible chains which are directed around end sprockets and carry an endless and continuous series of aluminum carrier slats. Each of the carrier slats has a center hole for receiving a vacuum from a manifold under the upper run and supports a corresponding shingle mold plate also constructed of aluminum. Each mold plate defines a cavity having a textured surface for the corresponding shingle and has opposite end portions with suction passages for progressively vacuum-forming the opposite upper and lower longitudinal portions of the sheet to define panels with hook-shaped lower portions and upper portions defining grooves for receiving the lower portions. As the conveyor continues to move, the vacuum-formed sheet is cooled, and edge portions of the sheet are trimmed.
In one embodiment, the upper portion of the sheet is reheated as the sheet separates from the mold plates on the endless conveyor, and the upper portion is folded back on itself to form a double wall nailing flange and a groove for receiving the hook-shaped lower portion of an adjacent overlapping siding panel. In another embodiment, reciprocating plugs assist in forming the hook-shaped lower portions and projections with undercut grooves within the upper portions adjacent a continuous nailing flange. The nailing flange is punched with longitudinally spaced slots, and the continuously moving sheet is then cut transversely at longitudinally spaced intervals to form a succession of elongated siding panels each having a length of about five feet.
Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.